In a fuel cell hydrogen (H2) and oxygen (O2) react with an electrolyte and emit heat to produce electrical energy and product water, which—together with condensed out humidifying water—must be removed from the fuel cell. This is done by blowing the water out of the fuel cell using excess process gas, for which reason it has to be supplied with more process gas than it requires for the reaction.
The active membrane and the electrodes of a PEM (Proton Exchange Membrane or Polymer Electrolyte Membrane) fuel cell enclosing it must be supplied evenly with process gases both on the anode side and on the cathode side, in order to achieve the most even cell activity possible over the entire active surface. Where the power densities are high, locally uneven activities result in local temperature increases and possible damage to the membrane and the electrodes.
The intake and egress of the two process gases into a fuel cell is realized by means of discrete channels, the geometry and position of which cannot always be configured in an optimum manner in relation to the active surfaces due to basic structural conditions. Therefore in both gas chambers of the fuel cell there are regions through which the flow is good and in which water is effectively eliminated and other regions, so-called flow shadows, where the flow is simply weak and the water is not satisfactorily eliminated. In unfavorable instances deposited drops of water can block the cell function in such flow shadows.
In fuel cells, which are operated with process gases with inert components, such as reformer gas or air, inert gas blankets foam in the regions with a poor throughflow, reducing the performance of the active components locally there. The fuel cell is then operated with a gas which has a low concentration of useful gas.
To resolve this problem US 2004/0151970 A1 proposes providing a structure made up of a large number of adjacent meandering channels rather than one larger gas chamber. However this results in a high gas pressure gradient in the fuel cell.
A fuel cell is known from DE 103 00 068 A1, in which the gas chambers are provided with oblong gas conducting elements. These conduct the process gases from a gas inlet to a gas outlet of the gas chambers in such a manner that they flow in particular through regions which would otherwise have a poor throughflow.
It is known from WO 03/081703 A2 that gas chambers can have narrow branches to achieve an even flow through the fuel cell.